Modern Vespa

I'm still plugging away at it. I've disconnected the battery, to try a reboot everything, no joy. I also pulled the ECM (engine control module) which looks brand new.

I gave it another shot of starter fluid and it did fire for a few seconds. Which is the first time I've had the happen in a long time. That's about my only positive data point.

This is bringing me back to thinking it's a fuel issue, either too much or none at all, more than likely too much.

I've ordered a new fuel tap from scooter west and well as a kit with the necessary hose clamps. Hopefully that will all arrive mid week.

I did notice many of the parts are stamped 14, leading me to believe the scooter is actually a 2015 model year, not a 2017. As I think about it I'm fairly sure it is a 2015. I believe the two model years were essentially the same.

I also now have an online copy of the service manual, which I've been combining for ideas.

I'm determined as ever to figure this out. I may try draining the fuel tank as I'm waiting on parts. Fresh fuel is a no brainer.

If you would kindly email that to me, I'll upload it to our archive at https://manuals.wotmeworry.org.uk/

Unfortunately I can't download it. I purchased viewing rights from AF1racing.com. I believe it was about $20. It requires I log in to my account before I can view the manual.

I admire the persistence. It's only a matter of time before you figure this out.

Drain fuel tank. Rinse the tank with new fuel. Drain it again. Remove petcock, and clean the filter that is on the petcock. Then refill the tank with fuel.

With the petcock in the tank, and both the fuel line and the vacuum line connected to the petcock, but both lines not connected to anything else (Carb and intake manifold, respectively), suck on the vacuum line. Does fuel flow out the fuel line? If so, good. If not, then you have some sort of vacuum line/fuel line problem. There is a filter in the vacuum line. Sometimes this can get plugged. If you have problems with these lines, just replace them both.

The next place to look is the intake manifold. It is where the suction for the vacuum line is coming from. If there is a crack in the intake manifold, then no suction. With your can of ether in one hand, engage the starter and spray ether all over the intake manifold. If there is a leak, the ether will get sucked into the cylinder and fire.

I think there is some sort of emissions system on your model year. Some people remove it.

Today's activities, I drained the fuel tank, flushed it with fresh gas. It's empty at the moment. Tank removal looked very complicated so I initially just used suction on the fuel tap. Once empty I tried removing the petcock, first removing the hose clamp. It's really firmly attached, not wanting to damage it I'm done trying to remove it.

The flow through the petcock is without any restriction and the fuel I drained was completely free of any particulate or debris. Both what I initially drained and after flooding the tank with another half gallon of fresh gas.

I've purchased new fuel line and new vacuum hose. I'm waiting on the hose clamp kit I ordered on Amazon, which should arrive on Thursday before trying to install these. I have a new fuel tap coming from Scooter West as well.

I'm debating whether or not to clean the carburetor, given I saw no particulate in the fuel and the the carburetor is essentially new, having maybe 50 miles on it, I'm thinking it adds more risk than it might mitigate.

One thing I am curious about is what appears to be a small filter of some kind in the vacuum hose that connects the fuel tap and the intake manifold.

Also, I did play around a lot with the fuel tap, as part of process of draining the fuel. It is definitely working as designed, what I can't tell is if the suction required to open the valve is within spec.

Lastly I've reassembled the handle bar cover and reattach the front storage locker. Once the new fuel tap and hose clamp kit arrive it won't take long to put everything back together and give it another try.

Fingers crossed this solves my problem.

FWIW, it doesn't take much suction to operate the fuel tap. You can give the hose a slurp with your mouth like a straw to confirm operation.

You can also bypass the current fuel, fuel tank, and fuel tap with a gravity-fed tube from a tank to the carb.

I don't think that's the problem here, though.

That's how I initially drained the tank. Used the vacuum hose like a straw. I was actually surprised how hard I needed to suck to actuate the valve. The equivalent of a very thick frap (the Bostonian term for a milkshake) where the straw just about collapses.

I could feel it actuate, I did this at least a dozen times. It's possible the fuel flow improved the more time I actuated it. The flow from the tap did seem to improve the longer the tank drained.

Also after the tank was empty I disconnected the fuel tap before adding a half gallon of fresh fuel. The flow rate then was definitely better than through the fuel tap. That's a qualitative assessment as I didn't actually measure the flow rates, which actually would be fairly easy to do, quantity per unit of time.

One more question, what is the black plastic filter looking thing that part of the vacuum line going between the fuel tap and the intake manifold? Air flows easily in either direction but light won't pass through it. Some kind of filter? Just curious.

I've been reading through the service manual and it has a minimum fuel flow rate specification and a simple way to confirm a flow rate.

To run the test place the fuel line in a container to collect the fuel, then run the starter for 5 seconds. The minimum flow rate is 22ml or 0.75oz under these conditions. This seems like a very simple test, which I'll try tomorrow with the current fuel tap. I'll rerun the test when the new one arrives so I can compare the results.

I'll also repeat the test a few times to check for variations. This will minimally allow me to partition things and better isolate root cause.

As I've said, it's not a complicated motor, somehow I'm being sloppy and missing something obvious.

BTW, the specification on the vacuum to open the fuel tap is 0.1 bar or 75 torr, the equivalent vacuum of about 1.5 psi, so not much.

That's the vacuum line filter. Some people say it's necessary. Others say no. I have mine still installed. You can imagine that it could become plugged and restrict the vacuum pressure on the petcock. That's why you might try a new vacuum line with no filter - see what happens.

Thanks, mine had some water in it. It's been super humid here, with the temperature going through the dew point a couple of times a day. I blew out the moisture. I'm also guessing it's somewhat directional in design. The service manual does show the orientation.

Somewhat frustrating day so far.

I did test the fuel flow with the old fuel tap and it's more than twice the 22cc minimum noted in the service manual. Being somewhat encouraged I reinstalled everything, put some gas in the tank and tried starting the scooter. The was one moment where it seemed like it wanted to start but that only lasted a second or so, then nothing.

Unfortunately it still won't start, even after trying starter fluid, again.

I pulled the spark plug and even put the old coil back, I'm seeing great spark with the plug grounded to the motor.

I pulled the carburetor off and it definitely got fuel in it. If I turn it on its side the fuel will drain out.

I also tried putting some starter fluid into the hose connection for the fuel tap on the intake manifold and got nothing.

I was convinced I am dealing with a fuel starvation issue, but I'm back to thinking it's electrical. Timing in particular.

Wow, this is a real stumper. Maybe by process of elimination it's time to start looking at the flywheel/stator to see if something is amiss from that end?

Double-check those valve clearances - this is a 4T, right?

It is a 4 valve motor, so yes.

If the valve clearances are out, you're on a hiding to nothing with any other possible faults, as it just won't run, or if it does, it'll stall very easily.

So double-check them! Especially with the 4-valve ones, if you think it's a bit tight, but 'OK' - it isn't, as the other valve on the same side will have closed up as you test. I like to use two feeler gauges on these, and a bit loose is better than a bit tight.

FWIW, as a quick test, I stopped up the vacuum port on the intake manifold and put my hand on the air filter side of the carburetor and ran the starter. I'm feeling a firm suction with each intake stroke of the motor.

I'm trying to find a video on checking the valve clearances. If anyone knows of one that's appreciated.